"A military column was driving by. All transport vehicles were ordered to stop to let the column pass...then a Priora [Lada] with a Chechen license plate whizzed by and an explosion happened," Turigin said.

In neighboring Chechnya, where Moscow has fought two wars against separatists since the mid-1990s, four men suspected of being Islamist fighters were killed by police earlier today, Interfax said, citing the Chechen Interior Ministry.

Also today, the Russian Interior Ministry said more than 600 terrorist acts were registered in Russia in the first nine months of this year, slightly up on last year, RIA reported.